calc the angle between two orientations?

CesiumJS
1

Hi all,

I’m trying to determine the difference in angle between two orientations in Cesium, which I’m sure is just my lack of quaternion math knowledge, but this seems like a common operation which could be considered for an addition as perhaps Cesium.Quaternion.computeAngleDiff(q1,q2)?

My understanding is that the quaternion defining the difference between two unit orientation quaternions q1+q2 is:

qDiff = inverse(q1) * q2

…and that you could then get the angle between q1+q2 as the angular component of qDiff.

Testing in sandcastle:

var q1 = Cesium.Quaternion.fromHeadingPitchRoll(new Cesium.HeadingPitchRoll(0, 0, 0));
var q2 = Cesium.Quaternion.fromHeadingPitchRoll(new Cesium.HeadingPitchRoll(5, 0, 0));

var q1inv = Cesium.Quaternion.inverse(q1, new Cesium.Quaternion());

var qDiff = Cesium.Quaternion.multiply(q1inv, q2, new Cesium.Quaternion());

var diffAngle = Cesium.Quaternion.computeAngle(qDiff);
console.log("diffAngleRad: " + diffAngle);
console.log("diffAngleDeg: " + Cesium.Math.toDegrees(diffAngle));

``

I get inconsistent results when I plug different values into the heading+pitch+roll values for q2.

I’m obviously misunderstanding how that should work, so it is more a quat math question than a Cesium question, but would anyone mind setting me straight on that, and thoughts on whether Quaternion.computeAngleDiff(q1,q2) would be a useful addition?

Cheers,

AC.

2

Hi AC,

Following this process the get the angle, it looks like you would use unit vectors (you can use the Cesium normalize function) and the conjugate.

Thanks,

Gabby